A REVIEW OF THE SIGNIFICANCE OF ANIMAL FOOD-PRODUCTS AS POTENTIAL PATHWAYS OF HUMAN EXPOSURES TO DIOXINS

The polychlorinated dibenzo-p-dioxins and dibenzofurans (dioxins) are groups of compounds with similar chemical and toxicological properties . Carcinogenicity was considered the most serious toxic end point when setting previous regulatory policies, but recent concerns have focuse d on the possible endocrine-disrupting activities of the dioxins. Toxi city is related to the 2,3,7,8 pattern of chlorine substitution, a pat tern that also leads to chemical and metabolic stability. Dioxins are practically insoluble in water and concentrate in lipids of biological systems, leading to low background concentrations in fat of the gener al human population. Major environmental sources of dioxins are emissi ons from industrial chlorination processes and combustion of materials containing chlorine. Inhalation and water have been ruled out as sign ificant exposure pathways, which suggests that food is the primary sou rce. Pathways of entry into food chains are atmospheric transport emis sions and their subsequent deposition on plants, soils, and water. The major food sources seem to be fat-containing animal products and some seafoods. This conclusion is based on evaluations of potential enviro nmental pathways involving dioxins and related compounds. Generally, d ioxins and other lipophilic compounds are not taken up and translocate d by plants, so residues in foods and feeds derived from seeds should be negligible. Animals on high-roughage diets, or those that ingest co ntaminated soil, are the most likely to accumulate dioxin residues fro m the environment. The conclusion that animal products are a major sou rce of human exposure requires verification by appropriate food sampli ng programs and animal metabolism studies. If it is desirable to reduc e human exposure to dioxins via the food supply, reduction of sources would be a more effective strategy than changing agricultural practice s and food consumption patterns.